1. Field of the Invention
The present invention relates to the field of computer image display, and in particular, to image protection.
2. Background Art
In the growing multimedia industry, a critical concern to image creators and image applications developers is image misappropriation, or piracy. Several pre-existing methods for protecting images from piracy have been developed, including watermarks, encryption and proprietary formats.
Watermarks are intentional imperfections in an image before or after it is converted to digital form. The resultant lack of quality in the image mitigates the desire to copy the image. However, watermarking is not satisfactory for imaging and multimedia products as it does not provide the high image quality required for marketable applications.
A more common method of image protection is encryption. Image encryption typically involves taking image data that exists in a standard format, such as GIF or BMP, and converting it into an unrecognizable data file through the use of a mathematical encryption algorithm. Prior to display, the encrypted image is passed through a deciphering process to regenerate the image data in a displayable format. The decrypted data is then placed in the video adapter's memory for use by the display unit.
Without encryption, image files in standard formats are recognized by a broad range of image processing applications. For this reason, unencrypted images can be copied and manipulated through unsanctioned applications. By encrypting computer files, use of the computer files can be restricted to only those applications provided with the deciphering scheme. Image files are therefore substantially protected from misappropriation up until the moment they are deciphered and placed in the video adapter's memory, where a video adapter is any device connected to the computer's data bus, including any local bus, that has its own memory or uses the computer's main memory to render images on a video display device. Once the image is present in the video memory in a standard display format, the image is again susceptible to piracy. Therefore, encryption is a necessary but incomplete protection scheme.
Proprietary formats are image data formats created for use in applications unique to the developer. These formats differ from an encryption scheme in that there often exists a one to one mapping between the source image file and the stored image file. Therefore, an expert may be able to recognize the nature of the data (i.e. that it is image data). In some cases, it is possible to reverse engineer the proprietary format and obtain the images. Further, some proprietary formats are available as part of developer tool kits. The format can be incorporated into a new application that is able to read or transfer proprietary image files.
Regardless of what encryption schemes or proprietary formats are used, an image file must eventually be translated into a standard image file format when it is supplied to the memory for the display unit. Once displayed, the image data sheds all security features. An end user can pirate the image by copying it from the video adapter's memory and storing it in any format. The pirated image data can then be distributed to other destinations.
For example, in the Windows.TM. operating environment sold by Microsoft Corporation, a user may pirate an image by pressing a "PRINT SCREEN" button on a computer keyboard and storing a bit-mapped image of the screen in a "clipboard." From the clipboard, the image can be "pasted" into an image processing application and stored for eventual unlicensed distribution. Therefore, though current encryption methods and proprietary formats are useful for securing image files, they are insufficient for protecting image files once they are provided to a video adapter's memory.
U.S. Pat. No. 4,241,415 to Masaki et al. discloses an apparatus for selectively masking portions of visual output. The apparatus contains a first memory for storing information code signals convertible into visible information and a second memory containing specific code signals in locations corresponding to the code signals in the first memory which selectively are not to be visualized. Signals from each memory are read simultaneously. When the device is in mask mode and a specific code signal is detected in the second memory, the corresponding information code signal in the first memory is masked, either by omission or replacement with a special mark. The Masaki patent does not suggest use of this apparatus in any security scheme.
U.S. Pat. No. 4,352,100 to O'Connell discloses an image formatting apparatus for use in changing image contrast or providing masked borders around selected images. The apparatus is not designed for security purposes. Further, it does not act to blank the selected image, but to blank the areas around it.
U.S. Pat. No. 4,554,584 to Elam et al. discloses an auxiliary circuit for remote control of television receiver blanking by digital code words transmitted as part of the video signal. The circuit allows the end user to determine what video signals to blank from the display unit.
U.S. Pat. No. 4,881,179 to Vincent discloses a method of controlling the unauthorized disclosure of classified data in a calendar application. Only those having a clearance code equivalent to or higher than the specified clearance code for the information can receive the calendar information. No apparatus is disclosed for preventing the copying of calendar images already present on the screen.
U.S. Pat. No. 4,932,053 to Fruhauf et al. discloses a safety device for preventing unauthorized detection of protected data in a memory chip by the use of current sensing approaches. Random current generators within the chip produce random current values on output pins of the chip to conceal actual current values that may indicate memory data values.
U.S. Pat. No. 5,036,537 to Jeffers et al. discloses a method for blocking out video signals in a television receiver. No means are disclosed to prevent copying of images that are allowed to reach the receiver.
U.S. Pat. No. 5,142,576 to Nadan discloses a key security system for selectively providing restricted information to video displays. An encoder transmits display update data and a key to a plurality of decoders. The decoder that matches the key receives the update data and places it in the picture store for a video display. No means are suggested for preventing the copying of images stored in the picture store of the video display.
U.S. Pat. No. 5,144,664 to Esserman et al. discloses a secure communication network serving a plurality of terminals grouped into different security categories. A headend device has several encryption algorithms stored. In addition, each terminal is coupled to a security element providing a decryption algorithm associated with one of the encryption algorithms stored in the headend. When security is breached, the headend switches to a new encryption algorithm and the security elements are replaced with new elements having a new decryption algorithm corresponding to the new encryption algorithm used in the headend. The object is to achieve inexpensive security system replacement in the event of a breach. The subject of copying images is not disclosed.
U.S. Pat. No. 5,208,857 to Lebrat discloses a method for scrambling and unscrambling image data by using the discrete cosine transform on blocks of data and by mixing these data blocks. The scrambled images must be unscrambled before being displayed in a video display unit.
U.S. Pat. No. 5,313,227 to Aoki et al. discloses a graphic display system capable of cutting out a partial image. The system includes image storage means, outline drawing means, mask data generator means, and partial image write means for writing into the image storage means only a portion of the source image which is not masked by the mask data. No means are described to prevent the copying of these stored images.